Can I still apply or am I shi- out of luck?

I was placed on unemployability by the VA with a rating of 70% totally and permanently disabled and paid at the 100% rate for VA compensation back in Dec. of 2002. I was told at that time that I may be eligible for SSDI. At the time I was comfortable with my VA compensation amount and figured why apply for SSDI when others could use the benefit more than myself. Well, 12 years later my VA comp does not go as far as it did and I am in significantly more pain as my body feels 75 and not the 55 that it actually is, and it gets worse and worse with each passing year. I have not been able to work in the same 12 years but someone told me that I had to have filed with-in 5 years of my disabilty and inability to work. Others have said, and from what I understand, I just had to have accumulated enough job credits for the 10 years prior to my inabilty to work from my disability. To me I saved SSDI 12 years of payments by deferring my entitlement as long as I possibly could. The only back pay I would want is from the day I apply for SSDI until the day of my first check. Does anyone have any info on this. I currently live outside the USA in Panama for the past 9+ years as to be able to be comfortable financially (and arthritically...lol) I relocated to a warmer, much cheaper location. Panama's cost of living has more than tripled over that time frame, so I could really use the extra income. Do not worry I still spend quite a bit of my compensation back home thru family and online purchases.